The present specification discloses a semiconductor memory device including a nonvolatile memory.
There is a prevalence of various small-sized and high-performance electronic equipment having a memory function, such as mobile terminal equipment and an IC card. With the prevalence, demand is rising for a semiconductor memory device capable of low-voltage and high-speed operation with low power consumption, suitably for such electronic equipment. The demand is particularly high for a nonvolatile memory. Typical representatives of the nonvolatile memory include a flash memory and a ferroelectric memory. The flash memory has the advantage that it allows a reduction in memory cell area, and can be formed as a small chip. However, the flash memory has the disadvantage that the number of rewrite cycles is smaller than that of a magnetic disc or the like.
The ferroelectric memory also has the advantageous properties of low power consumption and high-speed operation. Thus, each of the flash memory and the ferroelectric memory has the advantage of its own so that a technology for forming a semiconductor memory device from the flash memory and the ferroelectric memory will attract more attention in future.
For example, there is a technology which uses the ferroelectric memory as a substitute memory means for the flash memory depending on the frequency of rewrite operations to the flash memory for the purpose of compensating for the disadvantage of the flash memory, while taking the advantage thereof (see, e.g., Japanese Laid-Open Patent Publication No. HEI 7-281842). The technology allows a solution to the problem associated with the limited number of rewrite cycles of the flash memory.